In this episode, Captain Benjamin Sisko (Avery Brooks) and the crew travel back in time to prevent the assassination of Captain James T. Kirk (William Shatner) of the USS Enterprise by a Klingon using a booby-trapped tribble.

The cast of DS9 was dressed and coiffed to look like the cast of the original show. Here are O'Brien and Bashir with a tribble ...

It was neat how seamlessly‎ the characters of DS9 were inserted into the footage of the original episode. Here O'Brien and Bashir are inserted into this group of men Kirk is castigating ...

And at the end of the episode, Sisko was able to meet Kirk :) ...

Some of the funniest parts had to do with Worf, a Klingon character from DS9 - he was asked to explain why the Klingons of Kirk's era looked exactly like humans, and also to comment on the Klingon antipathy for soft furry cute harmless little tribbles ...

Worf: "They were once considered mortal enemies of the Klingon Empire. They were an ecological menace, a plague to be wiped out. Hundreds of warriors were sent to track them down throughout the galaxy. An armada obliterated the tribble homeworld. By the end of the 23rd century they had been eradicated."

You can actually watch the episode here where someone has posted it as a faux movie. It's a little fuzzy, but still ...